Method for extracting metals from ore

ABSTRACT

A process for extracting precious metals form ore that includes: collecting the ore, crushing the ore, enriching the ore using sulphuric acid at least in one washing cycle. Then precious metals are leached from the enriched ore by a non-aqueous solvent containing brome or bromide. The ore is than press filtered and direct electrical current is applied to the solvent bearing the precious metal, following which the metal is collected from the anode.

FIELD OF THE INVENTION

The present invention is in the field of mining and extraction of precious metals from ore. More particularly, the invention relates to extraction of gold and other metals from refractory ore.

BACKGROUND OF THE INVENTION

After the metal containing ore is collected from alluvium or bedrock, a variety of chemical procedures may be applied to extract the metals. If gold is the objective, a cyanide salt is typically used to solubilize the metal and leach it together with other metals from the ore. A common situation associated with extraction of the metal from gold ore, is observed in which the metal is locked in the ore. This phenomenon is referred to as refractory ore in which the small particles of the metal deposit are embedded in particles of minerals, metals and or organic matter, secluding the metal from the outside, thus preventing the active agent from accessing a considerable proportion of the metal deposit and leach it out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing the succession of steps carried out in order to extract precious metals from ore in accordance with one embodiment of the invention.

DESCRIPTION OF THE PRESENT INVENTION

The process of the present invention relates to extraction of precious metals from ore and particularly to the extraction from refractory gold ores. In general the process for the extraction of precious metals from ore is a sequence three procedures. First the ore is crushed, then enriched by washing away some constituents of the ore. Lastly the precious metals are leached from the enriched ore. In accordance with the present invention the ore bearing the metals, typically locked up gold, is preferably crushed to a substantially 0-26 mesh size particles. In a preferred embodiment of the invention, the crushing is performed using a hammer crusher, or a hammer mill, or both. The entire process of extraction according to a preferred embodiment of the invention is described schematically in FIG. 1 to which reference is now made. In step 20 the ore is collected. In step 22 the ore is crushed, preferably to grain size as described above. In step 24 the crushed ore is subjected to washing by sulfuric acid. This step can be repeated several times, typically by subjecting the ore to measured amounts of sulfuric acid. In step 26 the ore is leached by a non-aqueous mixture of solvents, the nature of which will be described below. The ore typically undergoes filtering to extract a remaining solvent containing ore in step 28. The solvent bearing the dissolved metal is subjected to the effect of direct electrical current which precipitates the metal ions on the anode. The anode is then treated mechanically at step 30 for the removal and recovery of the metal.

Other precious metals recoverable together and in addition to gold are typically, platinum, palladium, silver, and rhodium as well as manganese, copper, nickel, and less expensive metals such as iron, magnesium, zinc, and calcium.

A certain substantial proportion of the leached metals provided in the non aqueous solution in accordance with the process of the present invention is present in the form of nano-particles. Such nano-particulate matter may not bear electrical charge and must be recovered by such methods as applying mechanical force, by centrifugation or by sedimentation. Any cationic particulate matter, as well as the ions dissolved are recoverable from the leaching solvent by applying electrical current through the solvent.

Enrichment Solvent

The enrichment solvent used in accordance with the present invention is sulfuric acid. The sulfuric acid is applied typically in several cycles, at various degrees of concentration, for each cycle of washing a different concentration of the acid. Increasing the temperature of the sulfuric acid is implemented to enhance enrichment, typically temperature may reach as high as 400° C.

Leaching Solvent Mixture

As indicated above, the solvent mixture used for extracting the metals, typically gold, is non aqueous. The solvent is a mixture of bromine and a polar organic solvent. In a preferred embodiment of the invention the solvent is sodium bromide dissolved in alcohol rather than bromine. Other bromides used are potassium bromide, ammonium bromide or a mixture thereof. Typically methanol or ethanol are used in the solvent mixture.

Recycling of the Leaching Solvent

In the process of the invention care is taken to recycle the solvents, e.g. bromine, bromide and alcohol for reuse.

Retrieval of Constituents of the Enrichment Waste

The enrichment waste, i.e. the materials solubilised and/or otherwise extracted from the ore by the sulfuric acid, and removed from the ore, may be collected and used further as sources for commercial goods. For example, sulfates of metals such as calcium, magnesium, iron, aluminium and magnesium. In addition, silicates and phosphates may be made available as a result of the enrichment process. 

1. A process for extracting metals form ore comprising the steps of: collecting the ore crushing said ore; enriching said ore using sulphuric acid at least in one washing cycle; leaching said metals from said enriched ore by a non-aqueous solvent; press filtering said ore; applying direct electrical current to said solvent bearing metal, and collecting the metal from the anode.
 2. A process for extracting metals form ore as in claim 1 wherein said enriching is performed at several cycles, using a different concentration of sulphuric acid in at least one other cycle.
 3. A process for extracting metals form ore as in claim 1 wherein said crushed ore contains grains size of 0-26 mesh.
 4. A process for extracting metals form ore as in claim 1 wherein said non aqueous solvent is a mixture of bromine and a polar organic solvent.
 5. A process for extracting metals form ore as in claim 4 wherein said non aqueous solvent consists of bromide and alcohol.
 6. A process for extracting metals form ore as in claim 5 wherein said alcohol is ethanol.
 7. A process for extracting metals form ore as in claim 5 wherein said alcohol is methanol.
 8. A process for extracting metals form ore as in claim 1 wherein said ore is a refractory ore.
 9. A process for extracting metals form ore as in claim 1 wherein a proportion of said leached metal are present in the form of nano-particles.
 10. A process for extracting metals form ore as in claim 9 wherein mechanical force is applied to said leaching solvent to recover metal.
 11. A process for extracting metals form ore as in claim 2 wherein the temperature of said sulphuric acid is increased in at least one washing cycle. 